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1. Spatiotemporal patterns of extreme sea levels along the western North-Atlantic coasts

   https://doi.org/10.1038/s41598-019-40157-w  

   Muis, Sanne ; Lin, Ning ; Verlaan, Martin ; Winsemius, Hessel C. ; Ward, Philip J. ; Aerts, Jeroen C. J. H. ( March 2019 , Scientific Reports)

   The western North-Atlantic coast experienced major coastal floods in recent years. Coastal floods are primarily composed of tides and storm surges due to tropical (TCs) and extra-tropical cyclones (ETCs). We present a reanalysis from 1988 to 2015 of extreme sea levels that explicitly include TCs for the western North-Atlantic coastline. Validation shows a good agreement between modeled and observed sea levels and demonstrates that the framework can capture large-scale variability in extreme sea levels. We apply the 28-year reanalysis to analyze spatiotemporal patterns. Along the US Atlantic coasts the contribution of tides can be significant, with the average contribution of tides during the 10 largest events up to 55% in some locations, whereas along the Mexican Southern Gulf coast, the average contribution of tides over the largest 10 events is generally below 25%. At the US Atlantic coast, ETCs are responsible for 8.5 out of the 10 largest extreme events, whereas at the Gulf Coast and Caribbean TCs dominate. During the TC season more TC-driven events exceed a 10-year return period. During winter, there is a peak in ETC-driven events. Future research directions include coupling the framework with synthetic tropical cyclone tracks and extension to the global scale.

    

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2. Subseasonal Variability of Elevated Dust Concentrations Over South Florida

   https://doi.org/10.1029/2019JD031874  

   Kramer, S. J. ; Kirtman, B. P. ; Zuidema, P. ; Ngan, F. ( March 2020 , Journal of Geophysical Research: Atmospheres)

   Dust mass concentrations have been measured daily at Miami, Florida, in the summer months, and biweekly throughout the remaining months, since 1974. The 43‐year record of dust mass concentrations indicate large daily, seasonal, and interannual variations, with most of the dust arriving within 5–8 episodes each summer. On average, dust arrives to Miami, Florida, 10 days after emission from North Africa, with measured concentrations depending on characteristics of the lower free‐tropospheric winds due to the vast travel distance. Daily dust mass concentrations from July and August, the months that contribute the most to the annual mean, are used to characterize the synoptic conditions most favorable for dust transport. Two key regions are linked with the highest daily dust mass concentrations above Miami: (i) easterly winds, averaged over 850–500 mb, over the Tropical West Atlantic [15–25°N, 45–80°W], and (ii) southerly winds, similarly averaged, over the Florida Peninsula [20–30°N,75–80°W]. Winds within these two regions are enhanced when the North Atlantic subtropical high is displaced south and zonally elongated, relocating the western edge over Florida. A dust‐transport‐efficiency index, based on the maximum potential for dust to arrive above Miami with limited loss to deposition or mixing, identifies high‐dust loading cases on the subseasonal scale. Monthly dust‐transport‐efficiency values agree well with the monthly dust trends over the 43‐year time span. While seasonal dust loadings have been decreasing over Florida in the past decade, the transport efficiency has been increasing, possibly due to trends in the North Atlantic subtropical high.

    

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3. Unprecedented Expansion of the Azores High due to Anthropogenic Climate Change

   https://doi.org/10.5194/egusphere-egu22-3876  

   Ummenhofer, C. ( April 2022 , European Geophysical Union General Assembly 2022)

   The Azores High is a subtropical high-pressure ridge in the North Atlantic surrounded by anticyclonic winds that steer rain-bearing weather systems. The size and intensity of the Azores High modulate the oceanic moisture transport to Europe thereby affecting hydroclimate across western Europe, especially during wintertime. While changes in the North Atlantic storm track have been linked to the variability of the North Atlantic Oscillation (NAO), we focus on North Atlantic variability with a subtropical perspective by focusing on the Azores High independently of the Icelandic Low. The subtropical perspective provides a direct understanding of regional climate variability in the western Mediterranean and reveals dramatic changes to North Atlantic climate throughout the past century and can provide insight into the impact of future warming on the dynamics of the Azores High and associated hydroclimate. Here we show that winters with an extremely large Azores High are significantly more common in the industrial era (since 1850 CE) than in preindustrial times, resulting in anomalously dry conditions across the western Mediterranean, including the Iberian Peninsula. Climate model simulations of the past millennium indicate that the industrial-era expansion of the Azores High is unprecedented throughout the last millennium (since 850 CE), consistent with proxy evidence from Portugal. Azores High expansion emerges after the end of the Little Ice Age and strengthens into the 20th century consistent with anthropogenically-driven warming. 

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4. A Global Analysis of Interannual Variability in Potential and Actual Tropical Cyclone Intensities

   https://doi.org/10.1029/2020GL089512  

   Shields, Shannon ; Wing, Allison A. ; Gilford, Daniel M. ( September 2020 , Geophysical Research Letters)

   We examine the relationship between interannual variability of potential intensity (PI) and tropical cyclone (TC) actual intensity (AI) and the factors contributing to this variability across all global ocean basins. Using best‐track data and three reanalysis products from 1980–2016, we find that the Western North Pacific is the only basin that yields consistently significant correlations between AI and PI sampled along the TC tracks. In contrast to a previous study, the North Atlantic does not yield statistically significant correlations. This is because the correlation between AI and PI in the North Atlantic is sensitive to the length of the time period considered and the individual years within that time period. Both thermodynamic efficiency and air‐sea disequilibrium contribute to interannual variability in along‐track PI.

    

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5. Mangrove Damage, Delayed Mortality, and Early Recovery Following Hurricane Irma at Two Landfall Sites in Southwest Florida, USA

   https://doi.org/10.1007/s12237-019-00564-8  

   Radabaugh, Kara R. ; Moyer, Ryan P. ; Chappel, Amanda R. ; Dontis, Emma E. ; Russo, Christine E. ; Joyse, Kristen M. ; Bownik, Melissa W. ; Goeckner, Audrey H. ; Khan, Nicole S. ( April 2019 , Estuaries and Coasts)

   Mangrove forests along the coastlines of the tropical and sub-tropical western Atlantic are intermittently impacted by hurricanes and can be damaged by high-speed winds, high-energy storm surges, and storm surge sediment deposits that suffocate tree roots. This study quantified trends in damage, delayed mortality, and early signs of below- and aboveground recovery in mangrove forests in the Lower Florida Keys and Ten Thousand Islands following direct hits by Hurricane Irma in September 2017. Mangrove trees suffered 19% mortality at sites in the Lower Florida Keys and 11% in the Ten Thousand Islands 2–3 months post-storm; 9 months post-storm, mortality in these locations increased to 36% and 20%, respectively. Delayed mortality of mangrove trees was associated with the presence of a carbonate mud storm surge deposit on the forest floor. Mortality and severe branch damage were more common for mangrove trees than for mangrove saplings. Canopy coverage increased from 40% cover 1–2 months post-storm to 60% cover 3–6 months post-storm. Canopy coverage remained the same 9 months post-storm, providing light to an understory of predominantly Rhizophora mangle (red mangrove) seedlings. Soil shear strength was higher in the Lower Florida Keys and varied with depth; no significant trends were found in shear strength between fringe or basin plots. Rates of root growth, as assessed using root in-growth bags, were relatively low at 0.01–11.0 g m−2 month−1 and were higher in the Ten Thousand Islands. This study demonstrated that significant delayed mangrove mortality can occur 3–9 months after a hurricane has passed, with some mortality attributable to smothering by storm surge deposits. 

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